Synthetic rubberlike materials



1 Patented Sel g,

SYNTHETIC RUBBERLIKE MATERIALS 1 William 0. Must, Philadelphia. Chessie E. Belle berg, Gienside, and Charles H. Fisher, Abing ton, Pa allig'nors to the United States of America as represented by the Secretary of 7 'Agricuiture so Drawing. Application October 21, 1944,

i Serial No. 560,586

' Claims. (01. zoo-rat) leaned under the m of was a, 1883, as amended 'April :0, 1928;370 'o. o. m)

This application is made under the act of March 3, 1883,'as amended by the act of April 30, 1928, and the invention herein described; if patented, may be manufactured and used by or for the Government of the United States of America for governmental purposes without the-payment to us of any royalty thereon.

' vulcanization. Other objects and advantages of scription.

The present invention relates to synthetic rubfound in rubber and certain synthetic rubbers,

and several unsuccessful attempts have been made to transform the i flexible alkyl acrylate polymers into true synthetic rubbers. vulcanization does not occur when alkyl acrylate polymers such a polymethyl acrylate and polyethyl acrylate, are heated with sulfur. We have attempted vulcanization by heating such polymers containing sulfur and mixtures of such polymers, sulfur, carbon black and accelerators without successful results. Noappreciable change is broughtabout by heating such mixtures and the products lack many of the desirable properties found in vulcanized rubber and vulcanized synthetic rubbers.

An object of this invention is accordingly to produce vulcanized alkyl acrylate polymers havingenhanced rubberlike properties and capable of being used in place of rubber.

Afurther object is to prepare alkyl acrylate polymers which can be compounded and milled on standard rubber rolls and equipment and cured or vulcanized in standard rubber moulds to give vulcanizedrubberlike products.

A further object is to produce synthetic rubbers which have greater resistance to oils, oxidation and aging than natural rubber and some of the previously described synthetic rubbers.

A further object is to provide synthetic rubbers which can be made from carbohydrates, an

abundant and reproducible raw material.

A further object is to provide methods for copolymerizing methyl acrylate, ethyl acrylate and similar alkyl acrylates, particularly methods of polymerization which permit linear growth but prevent or retard cross-linkage, thus giving polymers having olefinic unsaturation available for our invention will appear-from the following de- We have found that synthetic rubbers can be made by copolymerizing methyl acrylate and other alkyl acrylates with small quantities of polyiunctional polymerants. such as allyl maleate, methallyl fumarate, allyl lactate maleate, crotyl acrylate, furfuryl acrylateyand furfuryl meth-' acrylate, mixing the resulting copolymers with sulfur, carbon black and vulcanizationaccelerators known to accelerate the sulfur vulcanization of natural rubber, and other materials commonly employed in the vulcanization of rubber, .and heating the resulting mixtures under the: general conditions commonly used to vulcanize rubber and other synthetic rubbers. We have found that the alkyl acrylate copolymer can be vulcanized when the copolymer is prepared from a monomer mixture containing an alkyl acrylate and a polyfunctional monomer in the proportion, by weight, of from to 98% of alkyl acrylate to at least 2% of the polyfunctional monomer, although as much as r of the latter can be used.

The copolymerization can be effected by using emulsion, mass, or solution polymerization methods to give vulcanizable alkyl acrylate copolymers. Although the polymerization can be conducted in the presence of known polymerization regulators which prevent or retard cross linkage and thus exert a beneficial effecton the process, such as certain mercaptans, acrylonitrile, or both (the use of dodecyl mercaptan and acrylonitrile being particularly satisfactory), and others such as carbon tetrachloride, hexachloroethane, xanthogen disulfide, and trichloropropionitrile, vulcanizable alkyl acrylate copolymers can be made without their use. I l

The methods used to convert alkyl acrylates into synthetic rubbers by-our invention will now be described, but it will be understood that the invention is not limited to these examples.

Emulsion polymerization was used in several instances to prepare the copolymers, but the copolymer may be made by solution or mass polymerization. Emulsion polymerization was used to prepare the polymers shown in the table. In experiment 23 the following method was used: The monomer mixture g. methyl acrylate, 10 g. 2-ethylhexyl acrylate and 5 g. allyl maleate) was added with stirring to a 500 ml. three-neck 'flask fitted with a reflux condenser, which contained ml. water and 2 g. of a soltuion of cetyl dimethyl benzyl ammonium chloride. The mixture was heated to refluxing temperature, al-

9,449,812 3 4 I lowed to cool until refluxing ceased, and small can be vulcanized by virtue of a small amount of quantities of 30 percent hydrogen peroxide (total, unsaturation. vulcanization or cross-linkage of 2 ml.) were added until polymerization started. our unsaturated alkyl acrylate copolymers can be The mixture was then allowed or caused to reflux effected by treatment with benzoyl peroxide and for one hour. After cooling, the polymer was 5 by similar methods. I agulated by 'the addition of small quantities of Vulcanizable alkyl acrylate-copolymers of the an acetic acid-calcium chloride mixture. The type described herein can be made by other methpolymer was washed and dried prior to comods which will occur to those skilled in the art. poundingandcurinm' I For example, a vulcanizable alkyl acrylate co- Using standard rubber rolls, the following inl polymer w uld e ain d y r ti a p lygredients were milled into 100 parts by weight of mer made from 95 parts methyl acrylate and 5 the copolymers: 0.5 part mercaptobenzothiazole, parts acrylyl chloride with an unsaturated alco- 5.0 parts zincoxide, 2 parts stearic acid, 2 parts hol, amine or mercaptan. A vulcanizable alkyl sulfur, 30 parts carbon black, and 1 part tetraacrylate copolymer could be obtained also by remethylthiuram disulflde. The compounded mixmoval of HCl from a copolymer prepared fromtures were cured in standard rubber moulds at about 95 parts of alkyl acrylate and about 5 parts about 298.F. for periods varying from 15 to 120 of vinyl chloride or some other halogen-containminutes. The cured products were soft and rubins monomer. As shown by our invention, any berlike. The tensile strengths and ultimate elonalkyl acrylate copolymer composed almost engations were as high as 1400 lbs. per square-inch tirely of alkyl acrylate units but containing oleand 800%, respectively.. finic double bonds may be vulcanized by the The allyl lactate maleate listed in the table was method herein outlined. Moreover, various prepared by allowing allyl lactate to react with emulsifiers, catalysts, stabilizers, and so forth, maleic anhydride. Other polymerizable esters may be used in the polymerization. and various containing two or more oleflnic linkages may be accelerators, fillers, pigments, extenders, and so made by condensing methallyl glycolate, alkenyl forth, may be used for compounding. lactates such as allyl lactate, crotyl lactate, Although it is preferred to use only a small prochloroallyl lactate and similar alkenyl hydroxy portion of the polymerizable ester containing two esters with phthalic anhydride. fumaryl chloride, or more oleflnic linkages, it is possible to use acrylylchloride, crotonic anhydride, furoic acid, larger proportions. For example. 2 to 10 percent adipic acid and similar compounds. These esters of crotyl acrylate is adequate when mixtures of may be polymerized with alkyl acrylates or monomethyl or other alkyl acrylate and crotyl acrylate "oleflnic acrylic esters according to our invention are copolymerized, but larger amounts of the to prepare vulcanizable acrylate copolymers. crotyl acrylate can be used. In extremecases it This invention is a valuable advance in the art is possible to polymerize the polyfunctional monoas it extends the range of known rubber substimer such as crotyl acrylate alone and then vultutes, giving'new substitutes for rubber which canize the unsaturated polymer. have in some respects advantages over rubber. As many apparently widely difl'erent embodi- Furthermore, the synthetic rubbers described ments of this invention may be made without deherein can be made almost entirely-through 40 parting from the spirit and scope thereof, it is to lactic acid as intermediate-from carbohydrates, be understood that we do not limit ourselves to an abundant, domestic and reproducible raw mathe specific embodiments thereof except as deterial, The source of the small amount of polyfined in the appended claims.

Tabla-Polymerization of acrylic esters in the presence of polyjunctional monomers 1 Cetyldimethyl Monomers, grams ag? x' Catalyst, ml.

Ethyl acrylate (90), allyl lactate maleate 1 (10) 160 2. 0 60 B30; (1;. Methyl acrylate (120), butyl acrylate (60), allyl lactate maleate (20) 260 3.0 80 H30; (1 Ethyl acrylate (500), allyl maleate 700 8. 5 30 H20! 5 5) Methyl acrylate (85), z-ethylhexyl acrylate (l0), allyl maleate (5) 150 2.0 HgOs 22) Ethyl acrylate (177.2), crotyl a late (12.8), acrylonitrile (l0; 250 3.0 40 ,0:

Methyl acrylate (6i), butyl acry ate (30), iurluryl acrylate (4 acrylonitrile (5)...- 250 2. 5 130 10s (8 6) 1 Hydrogen peroxide was a roximately 309' I Piggared by treating ally actate with maleic anhydride.

8 D ecyl mercaptan (0.25 ml.) also used.

functional polymerant' used in making the co- Having thus described our invention, we claim:

polymer is relatively unimportant because only no 1. A process of preparing a synthetic rubber small proportions are required and many types comprising heating a mixture containing, as can be used. It will occur to those skilled in the monomeric components, an alkyl acrylate and art that many polyfunctional monomers, such as allyl lactate maleate in the proportion, by weight, cinnamyl acrylate, allyl furoate, methallyl itacoof from 80 to 98% of the acrylate to at least 2% nate, allyl acid maleate, vinyl crotonate, furfuryl of the maleate, in the presence of dodecyl mer methacrylate, allyl ether, vinyl ether, divinyl bencaptan and hydrogen peroxide, to eifect copolyzene, and diallyl phthalate, can be usedinstead merization of the monomeric components, comof the monomers listed in the table to prepare a pounding the resulting copolymer with sulfur,- vulcanizable alkyl acrylate copolymers. The vuland heating the compounded mixture to eil'ect canizable synthetic rubbers made previously from vm m ti alkyl a rylates nta n ar pr po ti ns of uta- 2. A process of preparing a synthetic rubber diene and, hence, are essentially butadiene prodcomprising heating a mixture containing, as

Hots- Mor ve 11 1 p rt tha the e ynmonomeric components, an alkyl acrylate and thetic rubbers are unsatisfactory. Our products allyl lactate maleate in the proportion, by weight, are essentially alkyl acrylatecopolymers which of from to 98% of the acrylate to at least 2% of the maleate, in the presence of a polymerization regulator adapted to retard cross-linkage and a polymerization catalyst, to effect copolymerization of the monomeric components, compounding the resulting copolymer with a rubber vulcanizing agent selected from the group conssiting of sulfur and benzoyl peroxide, and heating the compounded mixture to effect vulcanization.

3.. A process of preparing a synthetic rubber comprising heating a mixture containing, as monomeric components, an alkyl acrylate and allyl lactate maleate in the proportion, by weight, of from 80 to 98% of the acrylate to at least 2% of the maleate, in the presence of a polymerization regulator adapted to retard cross-linkage, to efiect copolymerization of the monomeric components, compounding the resulting copolymer witha rubber vulcanizing agent selected from the group consisting of sulfur and benzoyl peroxide,

and heating the compounded mixture to effect vulcanization.

4. A process of preparing a synthetic rubber comprising heating a mixture containing, as monomeric components, an alkyl acrylate and allyl lactate maleate in the proportion, by weight, of from 80 to 98% of the acrylate' to at least 2% of the maleate, to effect copolymerization of the monomeric components, compounding the resulting copolymer with a rubber vulcanizing agent, selected from the group consisting of sulfur and benzoyl peroxide, and heating the compounded mixture to effect vulcanization.

WILLIAM C. MAST.

'CI-ICESSIE E. REHBERG.

CHARLES H. FISHER.

REFERENCES CITED The following references are of record in the file of this patent: 1

UNITED STATES PATENTS Number Name Date 1,121,134 Rohm l Dec. 15 1914 2,105,361 Nowak Jan. 11, 1938 2,202,846 Garvey et a1. June 4, 1940 FOREIGN PATENTS Number Country Date 7 496,276 Great Britain Nov. 28, 1938 OTHER REFERENCES V India Rubber World, April 1944, page 74. 

